In recent years, the textile industry has devoted considerable attention to the development of improved fluid weft insertion looms in which the weft strand is delivered through the warp shed by means of a stream of a fluid, such as air or water, emitted from a nozzle situated proximate to the shed, instead of by means of a shuttle projected from one side of the shed to the other and carrying a bobbin from which the weft strand is unwound as the shuttle moves through the shed. Such fluid weft insertion looms offer important advantages over shuttle looms in reducing the number of mechanical parts in the loom as well as the energy required for their operation and the noise produced thereby and making possible substantial increases in production speed. However, these advantages are accompanied by certain disadvantages, among which is the formation of a much inferior selvage construction.
In contrast to conventional weaving where a continuous weft thread is pulled back and forth through the shed by the shuttle, so that the ends of the weft are looped around the outside warp threads along the side edges of the fabric and anchored by sinuous engagement with the adjacent warp threads, giving a reasonably dense, tight, secure selvage construction, the weft strands in looms equipped with fluid insertion systems are nearly always projected from the same side of the fabric and each inserted length of weft is severed from the supply before the next weft strand is inserted. Consequently, the ends of the inserted weft extend loosely outside the confines of the warp, producing a so-called "fringe selvage".
In the absence of special measures, a "fringe selvage" tends inherently to be seriously susceptible to unraveling during further handling and processing. The warp threads are, of course, under more or less tension in the woven fabric due to the presence of the weft threads which forces them to assume a sinuous path. However, where the ends of the weft strand are loose at the extreme edges of the fabric and are thus free to bend away from the plane of the fabric, they offer little or no resistance to the inclination of the curved warp threads at those edges to straighten. Once a warp thread at the fabric edge has become straight, it remains so since there is no tension on the weft ends sufficient to overcome the straightening force of the warp and the fabric at this point becomes more open, allowing the looseness of the weft end to work inwardly to the next warp thread where the process is repeated.
While several techniques have been devised to prevent this problem in the past, as will be described more in detail later, all have proved to be less than satisfactory for various reasons, mainly a significant increase in the amount of yarns lost as waste.